1. Field of the Invention
This invention is directed to making chemical derivatives of carbon nanotubes and to uses for the derivatized nanotubes, including making arrays as a basis for synthesis of carbon fibers.
2. Related Art
Fullerenes are closed-cage molecules composed entirely of sp2-hybridized carbons, arranged in hexagons and pentagons. Fullerenes (e., C60) were first identified as closed spheroidal cages produced by condensation from vaporized carbon.
Fullerene tubes are produced in carbon deposits on the cathode in carbon arc methods of producing spheroidal fullerenes from vaporized carbon. Ebbesen et al. (Ebbesen I), “Large-Scale Synthesis Of Carbon Nanotubes,” Nature, Vol. 358, p. 220 (Jul. 16, 1992) and Ebbesen et al., (Ebbesen II), “Carbon Nanotubes,” Annual Review of Materials Science, Vol. 24, p. 235 (1994). Such tubes are referred to herein as carbon nanotubes. Many of the carbon nanotubes made by these processes were multi-wall nanotubes, i e., the carbon nanotubes resembled concentric cylinders. Carbon nanotubes having up to seven walls have been described in the prior art. Ebbesen II; Iijima et al., “Helical Microtubules Of Graphitic Carbon,” Nature, Vol. 354, p. 56 (Nov. 7, 1991).
Production of Single-wall Nanotubes
Single-wall carbon nanotubes (SWNT) have been made in a DC arc discharge apparatus of the type used in fullerene production by simultaneously evaporating carbon and a small percentage of VIII B transition metal from the anode of the arc discharge apparatus. See Iijima et al., “Single-Shell Carbon Nanotubes of 1 nm Diameter,” Nature, Vol. 363, p. 603 (1993); Bethune et al., “Cobalt Catalyzed Growth of Carbon Nanotubes with Single Atomic Layer Walls,” Nature, Vol. 63, p. 605 (1993); Ajayan et al., “Growth Morphologies During Cobalt Catalyzed Single-Shell Carbon Nanotube Synthesis,” Chem. Phys. Lett., Vol. 215, p. 509 (1993); Zhou et al., “Single-Walled Carbon Nanotubes Growing Radially From YC2 Particles,” Appl. Phys. Lett., Vol. 65, p. 1593 (1994); Seraphin et al., “Single-Walled Tubes and Encapsulation of Nanocrystals Into Carbon Clusters, “Electrochem. Soc., Vol. 142, p. 290 (1995); Saito et al., “Carbon Nanocapsules Encaging Metals and Carbides,” J. Phys. Chem. Solids, Vol. 54, p. 1849 (1993); Saito et al., “Extrusion of Single-Wall Carbon Nanotubes Via Formation of Small Particles Condensed Near an Evaporation Source,” Chem. Phys. Lett., Vol. 236, p. 419 (1995). It is also known that the use of mixtures of such transition metals can significantly enhance the yield of single-wall carbon nanotubes in the arc discharge apparatus. See Lambert et al., “Improving Conditions Toward Isolating Single-Shell Carbon Nanotubes,” Chem. Phys. Lett., Vol. 226, p. 364 (1994). While the arc discharge process can produce single-wall nanotubes, the yield of nanotubes is low and the tubes exhibit significant variations in structure and size between individual tubes in the mixture. Individual carbon nanotubes are difficult to separate from the other reaction products and purify.
An improved method of producing single-wall nanotubes is described in U.S. Ser. No. 08/687,665, entitled “Ropes of Single-Walled Carbon Nanotubes” incorporated herein by reference in its entirety. This method uses, inter alia, laser vaporization of a graphite substrate doped with transition metal atoms, preferably nickel, cobalt, or a mixture thereof, to produce single-wall carbon nanotubes in yields of at least 50% of the condensed carbon. The single-wall nanotubes produced by this method tend to be formed in clusters, termed “ropes,” of 10 to 1000 single-wall carbon nanotubes in parallel alignment, held together by van der Waals forces in a closely packed triangular lattice. Nanotubes produced by this method vary in structure, although one structure tends to predominate.
A method of producing carbon fibers from single-wall carbon nanotubes is described in PCT Patent Application No. PCT/US98/04513, incorporated herein by reference in its entirety. The carbon fibers are produced using SWNT molecules in a substantially two-dimensional array made up of single-walled nanotubes aggregated (e.g., by van der Waals forces) in substantially parallel orientation to form a monolayer extending in directions substantially perpendicular to the orientation of the individual nanotubes. In this process the seed array tubes are opened at the top (free) end and a catalyst cluster is deposited at this free end. A gaseous carbon source is then provided to grow the nanotube assembly into a fiber. In various processes involving metal cluster catalysis, it is important to provide the proper number of metal atoms to give the optimum size cluster for single wall nanotube formation.
Definition of Terms
“Fullerene carbon nanocages” is a term which encompasses fullerenes, buckyballs, carbon nanotubes, nested fullerenes, bucky onions, single-wall carbon nanotubes, multi-wall carbon nanotubes, and carbon fibrils.
“Endohedrally-doped fullerene carbon nanocages” refers to fullerene carbon nanocages (see above) which have something inside of them. That endohedral species can be an atom, a cluster of atoms, or a small molecule.
“Derivatized fullerene carbon nanocage” refers to a fullerene carbon nanocage which has atoms or functional groups (i.e., hydroxyl, methyl, phenyl, nitro, amino, etc.) covalently attached to the exterior of the fullerene carbon nanocage.
“Fluorinated fullerene carbon nanocage” refers to a fullerene carbon nanocage which has fluorine atoms covalently attached to the exterior of the fullerene carbon nanocage. This is a subset of the derivatized fullerene carbon nanocage mentioned above.
“Endohedral doping agent” refers to the species that is inserted into the fullerene carbon nanocage (or fluorinated fullerene carbon nanocage, or derivatized fullerene carbon nanocage) to generate an endohedrally-doped fullerene carbon nanocage (or an endohedrally-doped fluorinated fullerene carbon nanocage, or an endohedrally-doped derivatized fullerene carbon nanocage).
Derivatization of Single-wall Nanotubes
Since the discovery of single wall carbon nanotubes (SWNTs) in 1993 (Iijima, S. and Ichihashi, T., Nature 1993,363:603-605), researchers have been searching for ways to manipulate them chemically. While there have been many reports and review articles on the production and physical properties of carbon nanotubes, reports on chemical manipulation of nanotubes have been slow to emerge. There have been reports of functionalizing nanotube ends with carboxylic groups (Rao, et al., Chem. Commun., 1996,1525-1526; Wong, et al., Nature, 1998,394:52-55), and then further manipulation to tether them to gold particles via thiol linkages (Liu, et al., Science, 1998, 280:1253-1256). Haddon and co-workers (Chen, et al., Science, 1998, 282:95-98) have reported solvating SWNTs by adding octadecylamine groups on the ends of the tubes and then adding dichlorocarbenes to the nanotube side wall, albeit in relatively low quantities (˜2%). While theoretical results have suggested that finctionalization of the nanotube side-wall is possible (Cahill, et al., Tetrahedron,1996, 52 (14):5247-5256), experimental evidence confirming this theory has not been obtained.
Endohedrally-Doped Fullerene Carbon Nanocages
Endohedrally-doped fullerene carbon nanocages have captured the imagination of those in the bio-medical community. While the delivery of radioactive isotopes for biomedical applications (diagnostics and treatment) to specific targets inside living organisms is currently an important area of focus (radiopharmaceuticals), there exist many problems with regard to the chemical and radioactive instability of the compounds containing radioactive isotopes, and with the relatively high level of toxicity that these compounds possess.
Problems with the instability and toxicity of such radiopharmaceuticals can be overcome by encapsulation of the radioactive components into chemically and radioactively stable fullerene carbon nanocages, of which C60 is a prime example. Such nanocages can be covered by surfactants and specific targeting antibodies to make the structures soluble in water or other solvents and to achieve specific binding, e.g., to tumor cells. To protect these cage-containers from chemical destruction, to ensure their solubility and enhanced biocompatibility, and to facilitate the attachment of bio-specific ligands, a surfactant (e.g. Pluronics, a block ABA copolymer of poly(oxyethylene) and poly(oxypropylene)) can be used on the cage exterior.
Perhaps one of the most interesting fullerene carbon nanocage structures for such abovementioned endeavors are single wall carbon nanotubes (SWNTs), due to their unique dimensions and low-level of surface reactivity. While they are difficult to separate due to their strong affinity towards each other, surfactants have been shown to aid in their dispersal [A. Rinzler et al. “Large-Scale Purification of Single-Wall Carbon Nanotubes: Process, Product, and Characterization,” Applied Physics A, Vol. 67, p. 29 (1998)]. For biomedical targeting, the surfactant can be labeled with specific antibodies, such as tumor antibodies [K. Gonzalez et al. “Synthesis and In Vitro Characterization of a Tissue-Selective Fullerene: Vectoring C60(OH)16AMBP to Mineralized Bone,” Bioorg. Med. Chem., p. 1991 (2002)].
At present, there is no efficient way to synthesize fullerene carbon nanocage endohedral complexes (carbon cage-like molecular structures containing ions, atoms, or molecules within their interior). The main disadvantage of all currently known methods (high-temperature synthesis, irradiation with ion beams, high-pressure treatment of the carbon cages with gases like H2, He, etc.) is a very low synthetic yield (generally no more than ˜0.1%). In addition, encapsulation by direct irradiation with ion beams often results in the destruction of the cages. This is due to the fact that the ions must possess considerable kinetic energy to overcome the high potential energy barriers associated with ion penetration through the cage walls. Transfer of this energy to the cage can also result in fundamental changes of the chemical properties of the structure leading to cage destruction.
Insertion of uncharged species via treatment with high temperatures and pressures likely involves the breaking and subsequent reformation of carbon-carbon bonds during the insertion process. After insertion, the cage is thought to close up much like a self-sealing automobile tire. This process has been described previously [M. Saunders et al. “Noble Gas Atoms Inside Fullerenes,” Science, Vol. 271, p. 1693 (1996)] and produced somewhat higher yields (˜2%).
Direct high-temperature synthesis (arc synthesis using doped carbon rods) of such endohedral fullerene carbon nanocage complexes is extremely costly given that yields of the compound are very low (on the order of 1% or less) [Y. Chai et al. “Fullerenes with Metals Inside,” Journal of Physical Chemistry, Vol. 95, p. 7564 (1991)]. Furthermore, when endohedrally doping the fullerene carbon nanocages with a radioactive species (desired for bio-medical applications), one is faced with safety and environmental issues surrounding the production of radioactive pollution. Consequently, a more efficient method of endohedrally-doping fullerene carbon nanocages would be of great benefit.